SAN FRANCISCO — Prison authorities say a San Quentin death row inmate’s death is being investigated as a suicide.

Michael Lamont Jones, 44, was pronounced dead Monday. The cause of death is pending an autopsy.

Jones was sentenced to death in 1991 by a Riverside County jury for the 1989 murder of Herman Weeks, 24, during the armed robbery of a Domino’s Pizza store.

Jones had been on death row since January 2, 1992.

Since 1978, which is when California reinstated capital punishment, more than 60 condemned inmates have died from natural causes, two dozen have committed suicide, about a dozen have been executed in California and seven have died from other causes.